package geom

import (
	"math"
)

// PointF is an X, Y coordinate pair (floating point).
type PointF struct {
	X, Y float64
}

// ZeroPtF is initialized on (0, 0).
var ZeroPtF = PointF{X: 0, Y: 0}

// PtF is a shorthand function to create a point.
func PtF(x, y float64) PointF {
	return PointF{X: x, Y: y}
}

// Add adds q as a vector to p.
func (p PointF) Add(q PointF) PointF {
	return PointF{p.X + q.X, p.Y + q.Y}
}

// AngleTo calculates the angle [0..2*Pi) from point p to point q.
func (p PointF) AngleTo(q PointF) float64 {
	a := math.Atan((p.Y - q.Y) / (p.X - q.X))
	if q.X < p.X {
		return a + math.Pi
	}
	if a < 0 {
		a += 2 * math.Pi
	}
	return a
}

// Distance calculates the distance between points p and q.
func (p PointF) Distance(q PointF) float64 {
	return math.Sqrt(p.Distance2(q))
}

// Distance2 calculates the squared distance between points p and q.
func (p PointF) Distance2(q PointF) float64 {
	dx := q.X - p.X
	dy := q.Y - p.Y
	return dx*dx + dy*dy
}

// In tests if the point p is inside the rectangle r.
func (p PointF) In(r RectangleF) bool {
	if p.X < r.Min.X || p.X >= r.Max.X || p.Y < r.Min.Y || p.Y >= r.Max.Y {
		return false
	}
	return true
}

// InPolygon tests is the point p is inside the polygon q.
func (p PointF) InPolygon(q PolygonF) bool {
	var n = len(q.Points)
	var c = false

	var i = 0
	var j = n - 1
	for i < n {
		if ((q.Points[i].Y >= p.Y) != (q.Points[j].Y >= p.Y)) &&
			(p.X <= (q.Points[j].X-q.Points[i].X)*(p.Y-q.Points[i].Y)/(q.Points[j].Y-q.Points[i].Y)+q.Points[i].X) {
			c = !c
		}
		j = i
		i++
	}
	return c
}

// Sub subtracts q as a vector from p.
func (p PointF) Sub(q PointF) PointF {
	return PointF{p.X - q.X, p.Y - q.Y}
}

// To32 transforms the point p into a PointF32.
func (p PointF) To32() PointF32 {
	return PointF32{float32(p.X), float32(p.Y)}
}